Hybrid encoder system for position determination

Abstract

A linear and curvilinear encoder is provided in which absolute mechanical position and high resolution position determination can be obtained using a cart having a mover with “hybrid” teeth, configured in a curvilinear profile or shape, moving along a curvilinear track with a stator having teeth. The absolute mechanical position and high resolution position determination can be detected on the track by applying an excitation signal to a coil surrounding particular teeth of the stator to produce an electromagnetic (EM) field which can be influenced by the profile or shape of the teeth of the mover. A resulting pick-up signal can then be detected in a pick-up coil surrounding particular teeth of the stator with different harmonics in the pick-up signal corresponding to harmonics of the profile or shape of the teeth.

What is claimed is: 
     
       1. An industrial control system for moving objects, comprising:
 a track having curved and linear sections; 
 a stator disposed along the track, the stator having a plurality of teeth; 
 a cart for moving objects along the track, the cart having a mover portion having a plurality of teeth, wherein the teeth of the mover portion are arranged to face the teeth of the stator across a gap, and wherein the teeth of the mover portion have a curvilinear profile with first and second harmonics; 
 an excitation coil surrounding teeth of the stator, wherein an excitation signal provided to the excitation coil is operable to produce an electromagnetic (EM) field; and 
 a pick-up coil surrounding teeth of the stator, wherein presence of the cart in the EM field induces a pick-up signal in the pick-up coil with first and second harmonics caused by the first and second harmonics of the curvilinear profile of the teeth of the mover portion in the EM field for determining a fine position of the mover portion with respect to the stator from the first harmonic and a coarse position of the mover portion with respect to the stator from the second harmonic. 
 
     
     
       2. The system of  claim 1 , wherein the first and second harmonics of the curvilinear profile of the teeth of the mover portion provide magnetic pole pairs in the EM field. 
     
     
       3. The system of  claim 2 , wherein the first harmonic of the curvilinear profile of the teeth of the mover portion provides at least five magnetic pole pairs for inducing the second harmonic in the pick-up signal being at least a fifth order harmonic and the second harmonic of the curvilinear profile of the teeth of the mover portion provides one magnetic pole pair for inducing the first harmonic in the pick-up signal being a first order harmonic. 
     
     
       4. The system of  claim 1 , wherein the coarse position provides an absolute mechanical position of the mover portion with respect to the stator in a section of the track with lower resolution and the fine position provides a non-absolute mechanical position of the mover portion with respect to the stator in the section of the track with higher resolution. 
     
     
       5. The system of  claim 1 , further comprising a controller receiving the pick-up signal, wherein the controller executes a fast Fourier transform (FFT) of the pick-up signal to derive the first and second harmonics. 
     
     
       6. The system of  claim 1 , wherein the teeth of the stator have a rectangular profile. 
     
     
       7. The system of  claim 1 , wherein the pick-up coil is a first pick-up coil and the pick-up signal is a first pick-up signal, and further comprising a second pick-up coil surrounding teeth of the stator, wherein the EM field induces a second pick-up signal in the second pick-up coil with the first and second harmonics for determining the coarse and fine positions. 
     
     
       8. The system of  claim 7 , wherein the first and second pick-up signals provide sine and cosine measurements, respectively. 
     
     
       9. The system of  claim 1 , further comprising a plurality of controllers, wherein each section of the track provides an output to a controller for determining the coarse and fine positions and a direction of the mover portion with respect to the stator in a section of the track. 
     
     
       10. The system of  claim 1 , wherein the gap is defined by a trigonometric function. 
     
     
       11. A method for moving objects in an industrial control system, comprising:
 providing a track having curved and linear sections; 
 providing a stator along the track, the stator having a plurality of teeth; 
 providing a cart for moving objects along the track, the cart having a mover portion having a plurality of teeth, wherein the teeth of the mover portion are arranged to face the teeth of the stator across a gap, and wherein the teeth of the mover portion have a curvilinear profile with first and second harmonics; 
 providing an excitation signal to an excitation coil surrounding teeth of the stator to produce an electromagnetic (EM) field; 
 detecting a pick-up signal in a pick-up coil surrounding teeth of the stator, wherein presence of the cart in the EM field induces first and second harmonics in the pick-up signal caused by the first and second harmonics of the curvilinear profile of the teeth of the mover portion in the EM field; and 
 determining a fine position of the mover portion with respect to the stator from the first harmonic and a coarse position of the mover portion with respect to the stator from the second harmonic. 
 
     
     
       12. The method of  claim 11 , wherein the first and second harmonics of the curvilinear profile of the teeth of the mover portion provide magnetic pole pairs in the EM field. 
     
     
       13. The method of  claim 12 , wherein the first harmonic of the curvilinear profile of the teeth of the mover portion provides at least five magnetic pole pairs for inducing the second harmonic in the pick-up signal being at least a fifth order harmonic and the second harmonic of the curvilinear profile of the teeth of the mover portion provides one magnetic pole pair for inducing the first harmonic in the pick-up signal being a first order harmonic. 
     
     
       14. The method of  claim 11 , wherein the coarse position provides an absolute mechanical position of the mover portion with respect to the stator in a section of the track with lower resolution and the fine position provides a non-absolute mechanical position of the mover portion with respect to the stator in the section of the track with higher resolution. 
     
     
       15. The method of  claim 11 , further comprising executing a fast Fourier transform (FFT) of the pick-up signal to derive the first and second harmonics. 
     
     
       16. The method of  claim 11 , wherein the teeth of the stator have a rectangular profile. 
     
     
       17. The method of  claim 11 , wherein the pick-up coil is a first pick-up coil and the pick-up signal is a first pick-up signal, and further comprising detecting a second pick-up signal in a second pick-up coil surrounding teeth of the stator, wherein presence of the cart in the EM field induces the second pick-up signal in the second pick-up coil with the first and second harmonics for determining the coarse and fine positions. 
     
     
       18. The method of  claim 17 , wherein the first and second pick-up signals provide sine and cosine measurements, respectively. 
     
     
       19. The method of  claim 11 , further comprising determining the coarse and fine positions and a direction of the mover portion with respect to the stator in a section of the track. 
     
     
       20. The method of  claim 11 , wherein the gap is defined by a trigonometric function.